Surface wave generator



Sept. 12, 1961 D. coURsEN SURFACE WAVE GENERATOR R m N wm ms R U O C L. m V A D Filed July l, 1958 ATTORNEY United States Patent ice 2,999,458, l SURFACE WAVE GENERATOR David L. Coursen, Newark,V Del., assignor to E., I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware I Filed July 1, 1958, Ser. No. 745,873 3 *Claimsa (Cl. lill-122) The present invention relates to a novel high-explosive device wherein the natural detonation front is distorted; More particularly, the present invention relates to a surface wave generator, i.e., a high-'explosive device wherein a detonation front generated at one point is made to am've simultaneously at a plurality of points on a desired surface.

When a homogeneous mass of a high explosive is initiated at one point, the resultant detonation front proceeds outwardly from the point of initiation at uniform velocity in all directions. For example, in the case in which a spherical charge of a high explosive is initiated at its center, the detonation front travels uniformly through the charge as an expanding sphere, the front eventually arriving simultaneously at all points on the surface of the charge. When, however, the spherical charge is not initiated at its center but at an eccentric point such as a point near its surface, the detonation front in this second case initially constitutes an expanding sphere until the portion of the boundary nearest the point of initiation is reached. Thereafter, the front travels through the remainder of the charge as an expanding segment of a sphere, the radius of curvature 'of the segment at any given point in the 'charge being determined by the distance from the initiation point. In the third case, a nonspherical homogeneous mass of explosive, e.'g. a pyramid, centrally or eccentrically initiated, the detonation front proceeds in the same manner as in the eccentrically initiated spherical charge. It is obvious that in either case 2 or case -3 t-h'e detdnation front, because of its natural curvature, does not 'arrive simultaneously at all points on the surface of 'the lcharge but arrives at various times, depending upon the distance betwen each m'sh point and the "starting, or initiation, point.

In many applications of explosives besides blasting, it is desirable to employ an explosive lcharge wherein the detonation front arrives simultaneously at 1a plurality of predetermined points on one or AIn'or'e tsurfaces of ythe charge. For example, lU.Sv. Patent 2,604,042y (Cook, l. H., to Imperial Chemical Industries, Ltd., lul'y 22, 1952) describes a method whereby a metal surface is embossed by means of a plane fde'toatin -fo-nt, V4lie. a detonation front which i's distorted to varrive fsiultaneously at a plurality of points ton 'afsufacet The explosive charge used is a composite charge c'oil'sistirl'g of several different explosives, each having a different detonation velocity. The form of the charge -is such 'that not only a great deal of care lmust betake'n in correlating the different detonati'on velocities but also a large quantity of explosive material must be incorporated into'th'e charge. This large amount 'of explosive increases `the cost of the unit and, moreover, frequently resultsfin-the destruction of the adjacent v"metal sur-face due to the brisance of the explosive which is present-in such laifg'e quantities. Obviously, the provision of a charg'ee'apable of producing the desired distortion of the detonation front and yet consisting ofen inherently smaller quantity of explosive material is of great value in this application. Moreover, the use of s'uch a surface wave-generator is exceedingly valuable 'in basic investigations V'ofeirplosive phenomena. Forexample,'in'a-fundiamertfalstudy of the subjection of objects such as metal plates to explosive superpressures, i.e. the exceedingly high pressures a Patented Sept. 12, 1961 of short duration generated by a high explosive, a deter;v

mination of the effect of a plane detonation front is of interest. A prerequisite of such an investigation of course i's the availability of an explosive charge which not only will generate the .plane detonation front but also will not destroy the object subjected to the superpres= Slll'eS.

Accordingly, an object of the present invention is the provision of an explosive device wherein the detonation front generated at one point is directed to arrive simultaneously vat a plurality of points on a surface. Another object of the present invention -is the provision of a surface Wave generator wherein the quantity of explosive is held to a minimum. A further object of the present invention is the provision of a surface wave generator -in which only one explosive composition is required. A still further object of the present invention is the provision of a surface wave generator causing a minimum of damage to adjacent objects.

I have found that the foregoing objects may `ybe achieved whenI provide` as a surface wave generator la mass of -a cap-sensitive high explosive Within which mass are disposed at least six inert rod-shaped barriers, the barriers defining a continuousrmatrix of the high explosive and delimiting a series of paths from the initiation point to each of a plurality of finish points on`the base of the mass, each of the paths being of sufficient cross#v sectional areato support the detonation, the shortest detonation path being equal for each initiation pointtinish poi-nt route, the barriers being stacked in at vleast four parallel layers, thev barriers in each layer being parallel, coplanar, and separated by a gap of at least 0.3 millimeter, the barriers in each layer crossing perpendicularly the barriers in the immediately adjacent layers, and lying directly over the 4gaps between barriers in the Ynextto-nearest lower layerpeach barrier having a cross-seo tional area of at least 3 square millimeters and suflicient to prevent the propagation 'of the detonation through the barrier, theminirnum dimension' of each barrier 'being'at least l millimeter, the length of the barrier in any .given layer except the last Alayer being equal `at least to taaeitilewrl wherein n is the layer number and wml is the width of the barriers in the preceding layer, `the ylength of the bar riei in the last layer being equal at most te wherein N is the y total number of barrier layers and wN 1 is the width of the barriers in the next-to-last layer, the number of barriers in any vgiven layer except the last layer being equal to at least wherein n 'is the layer number, the number of lbarriers in the last `laye-r being equal at most to N 2[2N 34( 1) l wherein N is the tota-1 number of barrier layers.

The etere-described surface 4wave generator is based upon well-known principles. Namely, rs't, for every high-'explosive composition, there is a certain 'dimension (Width 'or thickness), most conveniently e'xpressed as the crosslstinal area, Vrequired to support a detonatin, the detnatio being found to travel midwaybetween Vthe edges of. this size area. Second, for every `high explosive of given cross-sectional area, the propagation 'of the damnation is diverted jby the interposition in the path of the explosive train of an inert barrier of certain dimensions. Therefore, the detonation travels only along those paths between a given initiation point and a given finish point which are of suicient cross-sectional area to support the detonation. In the absence of any inert barriers, the detonation travels directly, i.e. in a straight line, to the nish point. When barriers of suicient dimension to interfere in the detonation propagation are provided in its path, the detonation must travel around each barrier put in its way.

Thus, it can be readily seen that the detonation can be forced to take a predetermined and desired path in a mass of explosive containing a plurality of barriers. When the barriers are of suicient dimension to control the diversion of the detonation and are so di-sposed that the shortest paths from the starting (initiation) point to each of the finish points on a desired surface are equal in length, the detonation front arrives simultaneously at all the finish points on the desired surface.

In order to describe more completely the nature of the present invention, reference is made to the accompanying drawings, in which FIGURE l shows a front view of one embodiment of the surface wave generator of the present invention, the embodiment being constructed in the form of a cube.

FIGURE 2 shows a front view of another embodiment of the present device, this embodiment being constructed in the form of a pyramid.

Referring now to the figures in more detail, in FIG- URE 1, B represents the rod-shaped barriers which may be solid or in the form of air gaps, i.e. empty holes, E the mass of explosive constituting a continuous matrix in the device, and P the initiation point. The barriers B have a dimension and arrangement such that they divert the detonation and delimit paths having the cross-sectional area of explosive required to support detonation. In this embodiment, the individual barriers of maximum Width are located in the two uppermost layers, and the barriers decrease in width with increase in their number per layer.

In FIGURE 2, B, E, and P0 are as in FIGURE 1. In this pyramidal mass of high explosive, however, all barriers are of the same width.

In both embodiments, the barriers, at least six in number and in at least four parallel layers, are arranged so that the barriers in any given layer, which barriers are parallel, coplanar, and separated by a gap, cross perpendicularly the barriers in the immediately adjacent layer or layers and lie directly over the gaps between barriers in the next-to-nearest lower layer. Although the barriers in a given layer are noncontiguous, the adjacent parallel layers may be contiguous.

In the operation of either embodiment, the mass of explosive is initiated at point P0 by conventional initiation means, e.g. an electric blasting cap. The detonation thus generated travels through the explosive mass along the tortuous paths delimited by the barriers and arrives at the plurality of nish points on the base of the explosive mass. Since all possible shortest detonation paths between the initiation point and the finish points on the base are equal in length, the detonation front, which is traveling at uniform velocity, arrives simultaneously at every nish point on the base.

Obviously, therefore, the only critical features of the present invention are: (l) that the high explosive must be in the form of a continuous matrix, (2) that the barriers must be of sufficient cross-sectional area to prevent the propagation of the detonation through the barrier, (3) that the initiation point-finish point paths must be of suflicient cross-sectional area to support the detonation, and (4) that the shortest detonation path to the finish point on the base must be equal for each of the initiation point-iinish point routes, the arrangement of the barriers satisfying the afore-discussed requirements.

By fulfillment of all the above requirements, a variety of surface wave generators are prepared which function satisfactorily, the exact configuration employed being dependent upon such considerations as economics, the application in which the unit is to be used, and so on. For example, the FIGURE 1 embodiment may be preferred when the surface wave generator is to be used in an area of limited vertical space because it is of less height than the FIGURE 2 unit, although it requires the use of more explosive, with subsequent increase in cost, than does the FIGURE 2 embodiment. On the other hand, when space is not at a premium, the FIGURE 2 embodiment would -be preferred. It must also be stated that the cost of the FIGURE l embodiment can be ,reduced somewhat by cutting olf some of the explosive in the region of the uppermost layers, sucient explosive -being left, however, to cover fully the barriers. In this connection, it should be pointed out that the formation of the FIGURE 2 embodiment as a cube having an internal pyramid of barriers is feasible but in most cases undesirable, inasmuch as the additional explosive thus required would increase the cost of the unit and might damage adjacent objects.

The exact explosive composition used is not critical so long as the explosive material detonates at high velocity and can be formed into the necessary continuous matrix surrounding the barriers. Such explosives include, among others, PETN, RDX, HMX, pentolite (a PETN-TNT mixture), cyclotol (a RDX-TNT mixture), and tetrytol (a tetroyl-TNT mixture). Of these explosives, the binary mixtures are preferred due to the ease with which they can be formed into the continuous matrix as for example -by casting. To illustrate, the surface wave generator of the present invention may be prepared from pentolite or the like 'by stacking the rodshaped barriers in the required arrangement in a mold of the proper form, heating the barriers, pouring molten pentolite over the barriers, and then cooling. If air gaps are to constitute the barriers, the solid rod-shaped barriers, acting as forms, may be removed and reused. The units may also be formed in layers, i.e. one layer of the barriers may be positioned in the form, the explosive poured over and allowed to cool, and then the next layer formed and so on. Naturally, in practice, this preparation method will give a unit having noncontiguous layers. In the stacking step, a mechanical feeding and stacking device may be used, the design of which device is within the scope of the mechanical art.

As aforementioned, each of the barriers must be of sucient cross-sectional area to prevent the propagation of the detonation through the barrier.4 The barrier crosssectional area naturally is thus dependent upon the specic high explosive constituting the matrix and upon the specific material of the barrier, since the barrier crosssectional area necessary to prevent the propagation is a function not only of the explosive composition but also of the barrier material. I have determined that each of the barriers must have a cross-sectional area of at least 3 square millimeters to prevent propagation through the barrier, the minimum dimension of any barrier being at least 1 millimeter. However, inasmuch as the cross-sectional area is dependent upon the explosive composition and barrier material, the exact area is not a specific value. 'Ihe length of the barriers is dependent upon the barrier width and the number of the layer containing the given barrier, as expressed by the following mathematical relationships BN; @entrain-umm MN) 1 BNSEQ- l) Bn Eq 2) 2 2 2w1 w1 3 2 2wz y21m 4 410s 2103 5 41,04 3704 6 81115 3105 7 81116 4to@ 8 16101 4207 9 1610s 510s 10 32109 5109 1 The length of the barriers in the first layer is arbitrary.

2 These Values of course are eliminated by the requirements of the construction of the unit.

To achieve the desired results, at least 6 barriers in at least 4 parallel layers are required.

Mathematical expressions can be set forth llimiting the number of barriers required in |any given layer. Satisfactory performance is obtained lfrom the unit when the following equations concerning the .number of barriers per layer are satisfied:

wherein SN is the number of barriersin the last, or lowermost, layer and N is the total number of layers, and

wherein Sn is the number of barriers in any given layer except the last layer and n is the number of the given layer (neN). The following table shows some vof those values which satisfy Equations 3 and 4.

l'lhese values of course are eliminated by the requirements of the construction of the unit.

The number of barriers in the two lowermost layers and the proximity of the parallel barriers in all layers directly determine the number of finish points on the base of the unit. For example, taking the simplest case meeting the requirements of the present invention, i.e. six barriers in four layers, it can be seen that there will be four points at which the two barriers in the lowermost layer cross the two barriers in the immediately adjacent layer. For each cross point, the detonation is diverted four ways, the detonation being split into two segments upon arrival at the upper of the two barriers of the cross point, each of the two segments being split in two at larrival at the lower of the two barriers. In the case of the FIGURE l embodiment wherein the adjacent barriers of each layer are sufficiently `separated to provide a cross-sectional area of explosive sufficient to provide two detonation lpaths between every two parallel barriers, four finish points result from every cross point. Therefore, in the FIGURE l embodiment having four cross points, the detonation ultimately arrives at sixteen nish points. lln the unit of FIGURE l as shown, there are 64 points at which the barriers in the lower two layers cross, giving 64 4, or 256, finish points. `In the unit of FIGUIRE 2, however, the barriers in each layer are so close that the cross-sec- 6 only one detonation path, thus, one detonation segment of each pair between adjacent parallel barriers is cancelled out. Therefore, a FIGURE 2 unit having `six barriers will have nine finish points. lIn the unit of FIGURE 2 las shown, there are a total of 56 cross points in the designated layers and 72 finish points on the base, the number of finish points on the base being related to the number of barriers in the two lowermost layers in the following wherein Pf is the number of finish points, x is the number of barriers in one of the two lowermost layers, and y is the number of barriers inthe other of thetwo lowermost layers. feature, i.e. the number of finish points on the base, yimposes another factor which must be considered .in the design of `a unit for a specific application. For .certain applications, only nine nish points wouldbe required and :the FIGURE Z surface wave Igenerator of simplest configuration would be suitable. However, in other applications, more finish points lare necessary and the use of the FIGURE l unit or units having more barriers is required.

Inasmuch as the number of finish points per unit of area of the base of the device is related to the number of cross points and thus the number of barriers per unit area, control over Vthe number of nish points per unit area may be afforded by regulation of the size of the barriers. When only a few finish points, for example nine or slightly more, on a large surface area are required, the barriers used are relatively large in size and close together within layers. To increase the number of finish points on the same area,nthe sizeof the barriers is reduced and if desired the gap between barriers within the layer is increased. A large number of finish points on a small area may be provided by using very small barriers, for example those having a cross-sectional area of only three square millimeters when such cross-sectional area is suiicient to prevent propagation of the detonation through the barrier as determined by the specific explosive composition and barrier material used.

As 'afore-mentioned, the initiation point-finish point paths must be of suicient cross-sectional area to support the detonation. Since the exact cross-sectional area of Ithe explosive train required for support of the detonation is a direct function of the specific explosive used, no exact value for the specific cross-sectional area required can possibly be set forth. However, I have found that the cross-sectional area of an explosive train of a Very sensitive explosive is sufficient to support the detonation when the explosive material lls la gap of 0.3 millimeter between adjacent barriers in any layer containing more than one barrier, i.e. when the explosive train has a Width of 0.3 millimeter, the thickness of the barrier regulating the thickness of the explosive train and 'any thickness of barrier sufficient to prevent propagation of the detonation therethrough providing suicient thickness of this sensitive explosive when the train width is 0.3 millimeter to provide sufficient cross-sectional area for support for detonation. Therefore, I may state that the gaps between barriers should have a minimum width of 0.3 millimeter.

Either a solid inert material or air is suitable for use as the rod-shaped barrier. There exists a large variety of solid substances from which the specific material used in the barriers may be chosen from the viewpoints of economy, availability, ease of handling and the like. Such substances include metals such as lead, rubber, plastic, glass, wood, and so forth.

Although the invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations are possible without departure from the scope of the invention. I intend, therefore, to

be limited only by the following claims.

I claim: l. A sur-face wave generator wherein the natural dettional area between adjacent parallel barriers provides 75 onation front is distorted to arrive simultaneously at a plurality of finish points on a surface which consists of a mass of a cap-sensitive high explosive within which mass are disposed at least six inert rod-shaped barriers each of which barriers extends from a surface of said mass to` al1- Other surface of said mass, said barriers dening :a continuous matrix of said explosive and delimiting a series of paths from an initiation point to each of said finish points, each of said paths being of sui-hcient cross-sectional area to support the detonation, the shortest path from said viniti'ation point to any one nish point being substanially equal to the shortest path from said initiation point to any other finish point, said barriers being stacked in at least four parallel layers, the barriers in each of said layers being parallel, coplanar, and separated by a gap of at least 0.3 millimeter, the barriers in each of said layers crossing perpendicularly the barriers in the immediately adjacent layers and lying directly over the gaps between barriers in the next-to-nearest lower layer, each of said barriers having a cross-sectional area of at least 3 'square millimeters and sucient to prevent the propagation of the detonation through the barrier, the minimum dimension of any barrier being at least 1 millimeter, the length of the barrier in any given layer except the last layer being wherein n is the layer number and Wn 1 is the width of each individual barrier in the preceding layer, the length of the barrier in the last layer being equal to at least wherein N is the total number of barrier layers and WN 1 is the Width of each individual barrier in the next-to-last layer, the number of barriers in `any given layer except the last layer being equal to at least wherein n is the layer number, the number of barriers in the last layer being equal to at most wherein N is the total number of barrier layers.

2. A surface wave generator according to claim 1, wherein the barriers of maximum Width are located in the two uppermost layers, the barriers decreasing in width with increase in their number per layer.

3. A surface Wave generator according to claim l, wherein all barriers are of identical width.

References Cited in the le of this patent UNITED STATES PATENTS 

